This invention relates to machines for making filled packages, and more particularly, to package making machines of the type wherein a tube of packaging material is sealed successively along longitudinally spaced lines extending transversely of the tube and is supplied with charges of product introduced to the tube between successive transverse sealing operations.
The improved control system of the invention is capable of general application but is shown and described, by way of example, in association with a package making machine of the type commonly referred to as a vertical form, fill and seal machine. In this type of machine, the packaging tube is made by folding a web of packaging material and sealing its overlapped side edges. Thus, side sealing as well as transverse or end sealing is required and the machine illustrated includes a continuous hot belt side sealer although the invention is not so limited. In the description and claims which follow terminology such as "package" and "bag" is used and is intended to be generally synonomous with other like terms such as "pouch," envelope," etc. Terms such as "product" and "charges of product" refer to any of a wide variety of package fill which can be accommodated in vertical form, fill and seal machines. The charges of product may be weighed and successively discharged by an associated product feeder, the feeder may provide a volumetric rather than a weight determination of product charge, and other means may be employed in introducing charges of product, this including the manual dumping of product into a tube.
As will be apparent, it is important to have the capability of varying the length of bags produced to suit the weight or volume of product to be introduced to each bag, or to correspond to the length of each repeat of indicia which may be printed on the tube. Accordingly, it has been a common expedient to provide for some bag length adjustment, but in the older machines the adjustment is difficult to make and often requires shifting or replacement of timing cams or other mechanical parts, the adjustment thus requiring that the machine be stopped or in a "down condition." Further, bag length determining mechanism has been conventionally interrelated with the sealing mechanism in such manner that adjustment of bag length disturbs timing of the sealing function and renders adjustment of the sealing mechanism necessary in order to bring the machine back to a condition of proper operation at each new bag length. When, as is common in the older machines, the tube of packaging material is fed through the machine by a reciprocating end sealer, the jaws of the sealer serve not only to form the transverse end seals but also to grip and pull the tube through the machine as the sealer moves in one direction of its reciprocating motion. Thus, the tube feeding function and the end sealing function must be performed during the same portion of each bag making cycle, and the amount of time devoted to tube feeding during each cycle cannot be shortened beyond the minimal amount of time required to produce satisfactory end seals. If, in such machines, the tube is made by folding a web of sheet material into a tube with overlapped longitudinally extending side edges and then sealing the overlapped side edges to one another by means of a longitudinal seam sealer, the longitudinal seal forming operation is commonly performed during the return stroke of the end sealer when the tube is stationary. Thus, the end seal operation and the longitudinal seal operation occur in different portions of the bag making cycle and each requires an associated minimal amount of time to effect acceptable seals. That is, each bag making cycle must include a first minimal amount of time for making satisfactory end seals and a second minimal amount of time for making satisfactory longitudinal seals, and each cycle cannot be shortened in time beyond the sum of such two minimum time periods.
In my U.S. Pat. No. 4,023,327, CONTROL SYSTEM FOR PACKAGE MAKING MACHINE, a vertical form, fill and seal packaging machine is provided with a tube feeder in the form of selectively operable feed belts and with a stationary end sealer. The control system in this patent includes a feed timer for operating the belts and has the capability of bag length adjustment merely by manual adjustment of the timer, thus adjusting that portion of the cycle devoted to the tube feeding operation. Photoregistration tube feeding termination and resulting bag length adjustment is also provided for with the feed timer serving as an override. End sealer operation occurs during the remaining portion of each cycle of operation after termination of tube feeding operation and prior to a next succeeding cycle start signal. Cycle start signals are derived from a cam driven by the mechanical power source of the machine and/or its associated product feeder.
The machine and control system of the patent provides for improved accuracy and flexibility of control but is not wholly satisfactory. Cyclical operation of the control system is tied to and derived from the mechanical power source and thus control system cycle time and machine cycle time are not independently adjustable. Neither are the various portions of the cycle of operation subject to independent adjustment. With overall cycle time mechanically determined, and with end sealing time determined as the remainder of each cycle after feeding, wholly independent adjustment of end sealing time is unavailable. Further, similar limitations are imposed on other secondary operations of the machine.
It is the general object of the present invention to provide an improved control system for a vertical form, fill and seal packaging machine, or other packaging machine of the transverse tube sealing type, the system having the capability of independent feed time, end seal time and overall cycle time adjustment.
A further object of the invention is to provide an improved on-demand control system operable in response to a series of cycle start signals irrespective of the time interval between said signals.
A still further object of the invention is to provide an improved control system for effecting various secondary operations in a packaging machine of the type mentioned, said secondary operations being adjustable as to time of occurrence and/or duration within each cycle of operation.
A still further object of the invention is to provide an improved control system of the type mentioned capable of controlling a product dump device in a product feeder associated with the packaging machine, the timed occurrence of dumping within each cycle of operation being manually electrically adjustable.
A still further object of the invention resides in the provision of a control system of the type set forth wherein manual electrical adjustment of all the aforesaid functions is possible during operation of a packaging machine and its product feeder.
Other objects and advantages of the invention will be apparent from the drawings forming a part hereof and from the following detailed description and claims.